Postgres SELECT COUNT ... FOR UPDATE

Here is pseudo code for what I'm trying to do: rate_count = SELECT COUNT(id) FROM job WHERE last_processed_at >= ? current_limit = rate_limit - rate_count if current_limit > 0 UPDATE job SET state='processing' WHERE id IN( SELECT id FROM job WHERE state='pending' LIMIT :current_limit ) I have it working except for concurrency issues. When run from multiple sessions at the same time, both sessions SELECT and therefore update the same stuff :( I'm able to get the 2nd query atomic by adding FOR UPDATE in it's SELECT subquery. But I can't add FOR UPDATE to the first query because FOR UPDATE isn't allowed with aggregate functions How can I make this piece an atomic transaction?